1. Field of the Invention
The present invention concerns wheelchairs, related devices, and methods of use, particularly for personal mobility.
2. Description of Related Art
As an alternative to walking, jogging, or running to move about in the physical environment, the wheelchair serves as a suitable although limited transportation means and is a requirement of daily mobility for individuals with partial or complete impairment of sensory or motor function in the legs, hips, and lower torso.
During wheelchair propulsion, a user occupying a wheelchair engages in intermittent exertion of muscle-generated force at a lateral location relative to a longitudinal vertical plane passing through the center of the vehicle to direct the vehicle along a desired course. The user controls the speed and orientation of the wheelchair by gripping a pair of opposing pushrims, attached laterally to the drive wheels, with the hands and uses the arms to apply force against the opposing pushrims. During this process, contraction and relaxation of muscles in the user's arms and hands causes the elbow and wrist joints to undergo repeated and readily observable angular changes.
Propulsion of wheelchairs further involves the act of coasting, wherein the user occupying the wheelchair momentarily exerts muscle-generated force to propel the wheelchair and, following said exertion, the user assumes a relaxed, non-exerting disposition while the wheelchair continues moving along the desired course with the wheelchair bearing the full weight of the user.
Some wheelchairs alternatively employ levers, either attached to the wheel hubs or to the wheelchair frame, wherein the levers enable the transfer of muscle-generated forces to the wheels while also affording the user a propulsion and control means that does not require manual contact with the wheels, tires or pushrims. Such “lever-drive” systems may also serve to amplify human force via a drive train, such as with gears or sprockets, or simply by virtue of the mechanical advantage conferred by the length of the levers. Similar to the experience of using a pushrim-driven configuration, in the case of a lever-driven wheelchair the elbow and wrist joints likewise undergo repeated and readily observable angular changes.
The left and right sides of the wheelchair are driven in a substantially independent fashion so that forward bodily force exerted by the occupant, using a first arm, through a first drive wheel of the wheelchair produces forward movement of a first side of the wheelchair and little to no forward movement of a second side of the wheelchair. Likewise, forward bodily force exerted by the occupant, using a second arm, through a second, opposing drive wheel produces forward movement of the second side of the wheelchair and little to no forward movement of the first side of the wheelchair. Forces independently imparted to the opposing drive wheels thus enable the occupant to steer the wheelchair while also enabling braking and propulsion of the wheelchair along the desired course. In an alternative characterization thereof, motive forces are exerted by the user and imparted through rotation of each drive wheel, to the ground surface upon which the wheelchair rests, at substantially lateral locations relative to a longitudinal vertical plane passing through the center of the wheelchair.
Regardless of the manual propulsion means, a forwardly-directed force transmitted through rotation of each drive wheel to the ground surface is accompanied by rearward movement of the ground-contacting region of the drive wheel, resulting in forward movement of the respective side of the wheelchair. Through this method of operation, the wheelchair user is also afforded the ability to slow down, stop, turn, and reverse the wheelchair along its course, depending on the user's skill level, grip strength, overall limb and torso strength, coordination and balance. Forward propulsion over longer distances, navigating over obstacles in the outdoors, negotiating tight turns in confined spaces indoors, and an overall sense of awareness upon encountering surfaces both familiar and unfamiliar are all reflections of an intuitive process by which the concerted efforts of the left and right sides of the occupant's upper body regulate the speed and direction of travel of the wheelchair in a carefully controlled manner.
Active manual wheelchair users, upon encountering a variety of physical environments requiring different levels of physical exertion as well as varying degrees of maneuverability, experience a profound need for sufficient upper body strength, range of motion, and manual dexterity, as well as the ability to execute gross and fine motor movements simultaneously. Also inherent to wheelchair propulsion is the patterned repetition of movements required to attain and maintain a desired speed of travel: a practiced user instinctively applies the correct amount of forward push and at a pace that is appropriately measured to achieve and maintain the desired speed of travel, in response to an acquired sense of speed, acceleration, resistance due to friction of the tires contacting the ground, and the force of gravity acting against or in the direction of travel. The dynamic, kinematic and rhythmic components are, therefore, significant and interlaced aspects of wheelchair mobility.